1. Field of the Invention
The invention pertains to the field of pumps which increase the flow of molten glass through a manufacturing process. More particularly, the invention pertains to a pump that homogenizes and pressurizes the glass for use in production of a high quality glass sheet.
2. Description of Related Art
This invention relates to the manufacture of glass that is currently used for the production of TFT/LCD display devices that are widely used for computers now and are expected to be used for television sets in the future.
Present technology for continuous glass manufacturing processes relies on gravity to facilitate the flow of glass through the forming apparatus to the means of solidification. Additionally, the molten glass must be homogenized by a mixing device. A drawback of present technology is that the flow of glass solely by gravity limits the production rates that can be accommodated by a given factory configuration. The glass melting furnace must be located at a sufficiently higher elevation than the forming apparatus to produce the required pressure for the glass to flow through a given forming apparatus. Once a factory is built, the production limitations are defined.
The flow of glass solely by gravity limits the pressure available for forming glass in new and innovative ways, especially in systems requiring higher pressure. There are practical limitations in locating a glass furnace high above the forming apparatus and ducting the molten glass a large vertical distance to the forming apparatus. Present glass mixers and homogenizers require operation with the outlet flow at atmospheric pressure. The homogenizer must be located in the forehearth at the elevation of the melting furnace. Current homogenizing mixers also produce a trail of poorly homogenized glass that flows off of the bottom tip of the device. This defect is termed xe2x80x9ccordxe2x80x9d in the glass industry. To a lesser extent, the glass flowing around the device is not thoroughly homogenized.
Therefore, there is a need in the art for a pump which overcomes the shortcomings of the prior art.
The present invention facilitates the supply of highly homogeneous molten glass at higher than normal pressure to a manufacturing apparatus. This permits an increased range of operation and versatility in manufacturing apparatus design.
The molten glass pump system of the present invention can include one or more pumps, which form either a single-stage apparatus or are combined in series to form a multi-stage apparatus. The exact configuration depends on the required process pressure and the required degree of glass homogenization. Examples of the invention include an auger pump and a mixing auger pump which have varying degrees of mixing action, as well as a homogenizing pump which provides some pumping action but is primarily a homogenizer. All three pumps preferably include a centerline flow recirculation feature which remixes inhomogeneous glass into the incoming glass stream. A counter-rotating sleeve, which straightens the glass flow exiting the apparatus and provides an additional flow recirculation path, is also preferably included.
In the auger pump, an auger, a device which is used primarily for pumping, is used in the molten glass pump. The mixing auger pump utilizes a modified auger with increased homogenizing (mixing) action, but a decreased ability to generate pressure and flow. The mixing auger preferably has periodic cutouts in the auger flights. These cutouts allow glass to pass backward (leak) into another flow path and mix with glass in that passage. The homogenizing pump is primarily a homogenizer, but it also provides some pumping action. The homogenizing pump includes a multitude of propeller blades radially attached to a cylindrical housing. The molten glass is mixed by placing each row of blades so that the flow exiting one row of blades is subdivided as it enters the passages between the next row of blades. Homogenization is accomplished by repetitively subdividing the flow path.